AIDS, a recently described syndrome of immune deficiency, severe opportunistic infection, and Kaposi's sarcoma, is characterized by a progressive and seemingly inexorable destruction of helper/inducer T cells. It is an often fatal disease with a prevalence rapidly reaching large proportions. The epidemiology of AIDS suggests that it may be caused by an infectious agent, possibly Epstein-Barr virus (EBV). The main objective of this study is to determine the association between EBV infection and potential chromosomal abnormalities, also possibly related to EBV infection, in the development and prognosis of AIDS, Kaposi's sarcoma, and a benign lymphadenopathic syndrome (BLS) which may be a precursor to AIDS. The objective will be achieved through a longitudinal 4-year evaluation of patients with the above diseases. EBV-specific serologic and virologic studies, i.e., antibody responses to EBV antigens, prevalence and estimated quantity of EBV (transforming ability, EBV-DNA, or specific antigens) on cells and tissues from patients will be serially performed. The prospective study will include detailed cytogenetic studies to document the frequency, position of break points, and type of chromosomal aberrations in patients. The latter changes will be correlated witht he EBV findings. Two hypotheses which speculate on the mechanism by which EBV could induce these diseases will be tested. One hypothesis presupposes that AIDS patients mount an abnormal immune ("autoimmune") response to EBV in which helper cells are destroyed; the alternate hypothesis postulates that AIDS patients may have a peculiar T helper lymphocyte susceptibility to EBV infection which then results in a lytic infection of these cells or their elimination by a cytotoxic T cell response. Evidence of T cell infection with EBV will be studied by conventional assays. A co-culture assay based on EBV-specific T cell clone proliferation will be used to study possible "anti-helper cell" responses in AIDS and BLS. This study is expected to yield important information in the diagnosis, prognosis, and etiology of AIDS and its potential prodrome, BLS.